The invention relates to a profiled surface which is used as an abradable in flow machines and to a flow machine with an abradable of this kind. The profiled surface which is used as an abradable will be named an abradable for short in the following.
In flow machines such as airplane propulsion units, stationary gas turbines, turbocompressors and pumps it is necessary for a high efficiency that at the periphery of a rotor carrying rotor blades a sealing gap between the blade tips and the housing be very narrow during operation. With the use of abradables on the inner surface of the housing over which the tips of the rotor blades move, it is possible to produce minimum sealing gaps without the blade tips thereby being damaged. For high operating temperatures, which lie above about 800xc2x0 C., the abradables must be manufactured with a ceramic material, which is applied by means of thermal spraying methods, flame spraying or atmospheric plasma spraying. Through the admixing of a phase which can be burned out (polymer powder) to a ceramic spraying powder, a porosity of the abradable can be achieved thanks to which fine particles can be released from the surface of the abradable by the blade tips of the rotating rotor.
In ceramic abradables with a non-profiled surface the blade tips must usually be armored, for example through laser re-melting with the simultaneous addition of hard particles to prevent damage during the abrasion. Released abrasion particles must be able to escape from the sealing gap without substantial resistance. An abradable with a profiled surface is known from EP-A- 0 935 009. It was expected from the latter that abrasion particles could escape without problems from the sealing gap and that an armoring of the blade tips could be dispensed with. Tests showed however that material was abraded at the non-armored blade tips during the abrasion in a manner which led to a corrugated edge of the blade tips. A material ablation of this kind at the blade tips cannot be tolerated.
It is therefore an object of the invention to create an abradable which has an abradable surface and is suitable for non-armored blade tips. Profiled surfaces are formed by the blade tips as they remove abradable material.
The profiled surface is used in flow machines. In these machines blade tips move over the profiled abradable in a predetermined direction. In so doing they produce a partial surface, an abraded surface, which is formed by the removal of material. The profiling of the surface is formed by ribs which surround chamber-like depressions. A rib direction can in each case be associated with the ribs. The abraded surface forms a pattern which is built up of strip-like elements and the elements of which lie in the directions of the ribs on connection lines between corner points of a reference grid. Largely at each location of the abraded surfacexe2x80x94i.e. at least at 80% to 95% of the abraded surfacexe2x80x94the rib direction differs from the direction of movement of the blade tips. For at least two-thirds of the abraded surface the direction of movement deviates from the rib direction by more than 30xc2x0, preferably more than 45xc2x0. The strip-like elements of the abraded surface can be curved as well as discrete and/or partly connected strips.
Thanks to the design of the profiling of the abradable in accordance with the invention, which is carried out taking the direction of movement of the blade tips into account, less material is removed at the non-armored blade tips and, in addition, the material removed is uniformly distributed over the entire edge of a tip. In order to reduce the material removal at the blade tips still further, the blade tips can also be armored.
The invention will be explained in the following with reference to the drawings.